CN110646818A - High-sensitivity satellite navigation fine-capturing method - Google Patents
High-sensitivity satellite navigation fine-capturing method Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
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Abstract
The invention discloses a high-sensitivity satellite navigation fine-capturing method. The common acquisition method of parallel correlation + FFT (fast algorithm of discrete fourier transform) has been widely used in satellite navigation. The invention adopts a parallel correlation and FFT method for delaying the output of correlation results, which can greatly save the register which needs to latch the correlation values after the completion of multipath correlation, thereby reducing the occupation of logic resources of FPGA; meanwhile, a special method is used for eliminating the influence of data bits (such as NH codes of BD 2) of partial satellite signals on the correlation length, so that the correlation length of data and pseudo codes is increased, and the aim of improving the capturing sensitivity is fulfilled.
Description
Technical Field
The invention belongs to a signal processing method of a satellite navigation receiver, and particularly relates to a high-sensitivity satellite navigation fine-capturing method.
Background
Satellite navigation systems (Beidou, GPS, GLONASS, etc.) are high-precision navigation positioning systems. The satellite receiver receives satellite signals through the receiving antenna to perform down-conversion processing on the satellite signals, then performs baseband digital signal processing on the down-conversion signals, and can give accurate information such as longitude, latitude, altitude, speed, time and the like after navigation resolving processing. At present, satellite navigation is widely applied to the fields of military affairs and civil use.
The baseband digital signal processing mainly comprises the functions of capturing and tracking satellite signals and the like. Due to algorithm limitations, the acquisition sensitivity is generally much lower than the tracking sensitivity, making it critical to improve the acquisition capability of satellite navigation signals. When acquiring satellite signals, especially when acquiring long codes, it is more essential to have a fine acquisition function. A good fine-capture method occupies a small amount of FPGA resources, but can greatly reduce the false alarm probability and improve the traction success rate.
The current widely used fine capture method is to improve the fine capture sensitivity by adopting 1ms (correlation operation of minimum unit) coherent integration and multiple times of incoherent integration, and the problems brought by the method are as follows:
(1) long-time non-coherent integration is needed to achieve higher sensitivity;
(2) the long-time incoherent integration cannot meet the satellite signal acquisition of a high dynamic scene;
(3) long-time incoherent integration acquisition time is long.
Disclosure of Invention
The invention aims to provide a high-sensitivity satellite navigation fine capturing method, which improves the fine capturing sensitivity without increasing the capturing time and meets the high dynamic requirement by improving the coherent integration time.
The invention is realized in such a way that a high-sensitivity satellite navigation fine-capturing method comprises the following steps:
step 1: generating a channel local code and setting a carrier frequency;
step 2: i, Q two-path mixing results are generated;
and step 3: I. performing multi-path short-time correlation operation on the Q two paths of signals and a local code;
and 4, step 4: storing the result of the multi-path correlation operation;
and 5: carrying out correlation operation on the short-time correlation result and the data jump coefficient;
step 6: performing FFT on the correlation operation result;
and 7: and performing modulus operation on the FFT result and outputting a capturing result.
The step 1 comprises the following operations:
the code phase obtained by rough capture is placed in a tracking channel, the channel code phase is delayed by stopping a channel code generator (the long code is the code generated by a chip waiting for the time to be placed in a relevant chip), and the local code is adjusted to be advanced by the rough capture result by L chips;
and obtaining Doppler frequency f0 according to coarse capture, placing f0 in a tracking channel, adjusting the carrier frequency of the corresponding tracking channel to be f (initial frequency of a local carrier) + f0, and simultaneously generating I, Q two paths of orthogonal carrier signals of corresponding frequency.
The step 2 comprises the following operations:
and performing correlation operation on the I, Q two paths of orthogonal carrier signals and the intermediate frequency signal to generate I, Q two paths of mixed frequency signals.
The step 3 comprises the following operations:
and carrying out N-path chip delay on the local code output by the tracking channel to generate N-path parallel code output, carrying out correlation operation on the N-path parallel code and the input I, Q two-path signals, respectively carrying out N-path short-time accumulation on N-path parallel correlation results, and finally delaying and outputting the N-path short-time accumulation results.
The step 4 comprises the following operations:
outputting N groups of short-time correlation results to the RAM after each acc _ complete (the signal is a first short-time correlation completion mark) is high, completing the write operation after N clocks, and performing M write operations by capturing once, wherein the depth of the RAM is M x N.
The step 5 comprises the following operations:
and correspondingly multiplying the short-time correlation result cached in the RAM by a data jump coefficient prestored in the ROM to generate a new short-time correlation result.
The step 6 comprises the following operations:
and (5) performing FFT operation on the data subjected to correlation operation in the step (5), and performing Q-point FFT operation (wherein Q is more than or equal to M) for P times N times in each capturing.
The step 7 comprises the following operations:
and performing modulus operation on the FFT result, comparing the maximum value, and keeping the capture code phase value and the Doppler frequency value corresponding to the maximum value.
And 3, performing N-path chip delay on the local code output by the tracking channel in the step 3 to generate N-path parallel code output, performing correlation operation on the N-path parallel code and the input I, Q two-path signals, performing N-path short-time accumulation on N-path parallel correlation results respectively, and finally completing marking control on the N-path short-time accumulation result delay output through the N-path short-time correlation.
In the step 5, the short-time correlation result cached in the RAM is correspondingly multiplied by a data jump coefficient prestored in the ROM in advance to generate a new short-time correlation result.
The invention has the advantages that (1) a parallel correlation and FFT method (see step 3) for delaying and outputting correlation results is adopted, so that registers for latching correlation values after completing multipath correlation are greatly saved, logic resources of an FPGA are reduced, and system power consumption is reduced; (2) a method for multiplying a data jump coefficient read from a ROM and a correlation result is used (see step 5), and the limiting influence of satellite signal data jump or NH code jump and the like on the correlation length is eliminated, so that the data phase and the pseudo code phase are improved.
Detailed Description
The invention will now be described in detail with reference to specific examples:
the principle of the invention is as follows: the method comprises the steps of conducting N-path chip delay on a local code output by a tracking channel to generate N-path parallel code output, conducting correlation operation on the N-path parallel code and an input baseband signal, conducting N-path short-time accumulation on N-path parallel correlation results respectively, finally conducting delay output on the N-path short-time accumulation result, multiplying the result by a data jump coefficient read out from a read-only memory (ROM), conducting Fast Fourier Transform (FFT) conversion, conducting modulus comparison on a conversion result to obtain a maximum value, and finally latching a code phase and a Doppler frequency corresponding to the maximum value and the maximum value. The method specifically comprises the following steps:
step 1: generating channel local code, setting carrier frequency
And adjusting a tracking channel according to the code phase obtained by rough acquisition, wherein the tracking channel is adjusted by delaying the channel code phase (the long code is the time-setting code to a relevant chip to wait for the chip to generate the code) by suspending the operation of a channel code generator, and finally, the local code is adjusted to be L chips ahead of the rough acquisition result.
The carrier Doppler frequency f0 is obtained through rough capture, the frequency f0 is converted into a cost to be added into a voltage-controlled oscillator of a tracking channel in an incremental mode to adjust the carrier frequency of the tracking channel, the carrier frequency after channel adjustment is adjusted to be f (initial frequency of a local carrier) + f0, and I, Q paths of orthogonal local carrier signals of corresponding frequencies are generated at the same time.
Step 2: generates I, Q two-way mixing results:
and (3) mixing the I, Q paths of orthogonal local carrier signals output in the step (1) with intermediate frequency signals of which the radio frequency front ends are subjected to digital signal processing respectively to generate I, Q paths of mixing results.
And step 3: I. and performing multi-path short-time correlation operation on the Q two paths of signals and the local code:
and (2) performing N-path chip delay (generally, N is 2 × L × TCODE/TCLK, wherein TCODE is the duration of one chip, and TCLK is the period of a working clock) on the local code output by the tracking channel in the step (1) to generate N-path parallel code output, then performing correlation operation on the N-path parallel code and the input I, Q-path signals, performing N-path short-time accumulation on N-path parallel correlation results respectively, and finally controlling the N-path short-time accumulation result delay output through an N-path short-time correlation completion mark.
The method comprises the following specific steps:
(1) when the correlation result of the immediate path (the 1 st path is not delayed) is accumulated to the last 1 working clock period of the time length of T0(ms) each time, 1 accumulation completion signal acc _ complete with high level of only 1 working clock period is generated, when acc _ complete is 1, the accumulation result of the immediate path is output, and meanwhile, the accumulation value is set as the current immediate correlation value, and the next round of accumulation operation is started;
(2) outputting the accumulation result of the delay 1 path in the last 1 working clock period when the acc _ complete is in the high level, setting the accumulation value as the correlation value of the current delay 1 path, and starting to perform the next round of accumulation operation;
(3) outputting the accumulation result of 2 paths of delay in the last 2 beats of high level of acc _ complete, setting the accumulation value as the correlation value of the current 2 paths of delay, and starting to perform the next round of accumulation;
(4) outputting the accumulation result of delaying N-1 paths until the subsequent N-1 beats when the acc _ complete is high level, setting the accumulation value as the related value of the current delaying N-1 paths, and starting to perform the next accumulation; namely, 1 time of N short-time correlation operation is completed;
(5) the same operation as above is performed when the next acc _ complete arrives until the correlation operation of T1(ms) is completed (the operation is performed M times, M × T0＝T1T0 must be divisible by 1);
(6) by the methods of (1) - (4), the correlation results of N paths are not calculated at the same time, but short-time correlation results of one path are calculated sequentially by each clock in N working clocks after acc _ complete is at high level, and the short-time correlation values are cached in the RAM (the short-time correlation results only store 1 clock and then start to participate in the next correlation accumulation operation, so the values are input into the RAM once being output); the acc _ complete completes the output of N paths of correlation results once after N working clocks with high level;
(7) the same operation as above is performed when the next acc _ complete arrives until the correlation operation of T1(ms) is completed (the operation is performed M times, M × T0＝T1T0 must be able to divide by 1).
And 4, step 4: storing results of multipath correlation operations
Inputting the N groups of short-time correlation results output in the step 3 into the RAM in N working clocks with high acc _ complete each time, and finishing the write operation after N clocks; and performing M write operations for one capture, wherein the RAM depth is M N.
And 5: performing correlation operation on the short-time correlation result and the data jump coefficient
The short-time correlation result cached in the RAM is correspondingly multiplied by a data jump coefficient prestored in the ROM, and the specific steps are as follows:
(1) and reading the short-time correlation result from the RAM, circularly reading a pre-stored first group of data jump coefficients from the ROM at the same time, wherein the read enable signals of the RAM and the ROM are consistent, and the reading of Q-M working clocks is stopped after every M working clocks are read. The initial value of the read address of the RAM is 0, 1 is added all the time when the read enable is high, accumulation is stopped when M × N-1 is added every time, and the address is set to be 0; the initial value of the read address of the ROM is 0, 1 is added every 1/T0 working clock addresses when the read enable is high, the address is set to be 0 when the address is added to T1-1, and the addition is restarted, and the operation is circulated for N times. After the above steps are carried out, the N short-time correlation results in the RAM are subjected to positive and negative judgment according to the data jump coefficient corresponding to the 1 st group read in the ROM in a circulating way, when the data jump coefficient is 1, the correlation results are output in a negative mode, and when the data jump coefficient is 0, the correlation results are output in a positive mode;
(2) and (3) sequentially operating as (1) until the P time, reading the short-time correlation result from the RAM, circularly reading the pre-stored P-th group data jump coefficient from the ROM at the same time, enabling the read signals of the RAM and the ROM to be consistent, and stopping reading Q-M working clocks after reading M working clocks. The initial value of the read address of the RAM is 0, when the read enable is high, 1 is added all the time, and the accumulation is stopped when the read enable is added to M × N-1 every time, and the address is set to be 0; the initial value of the read address of the ROM is (P-1) T1, when the read enable is high, 1 is added every 1/T0 working clock addresses, when the address is added to P T1-1, the address is set to 0, and the addition is restarted, and the operation is circulated for N times. After the above steps are carried out, the N short-time correlation results in the RAM are subjected to positive and negative judgment according to the data jump coefficient corresponding to the P group which is read from the ROM in a circulating way, when the data jump coefficient is 1, the correlation results are output in a negative mode, and when the data jump coefficient is 0, the correlation results are output in a positive mode;
(3) the ROM buffer depth is T1 × P, P × N sets of correlation results are generated altogether, each set of M correlation results, wherein the setting method of the ROM data hopping coefficient takes a GPS signal with a length of 20ms as an example (other satellite signals are sequentially expanded) as follows: considering the possibility of GPS data hopping, since the GPS data bit is 20ms long, there are 20 possibilities, so T1 is equal to 20(1ms number) and P is equal to 20 (data hopping possibility), as shown in table 1.
GPS signal of table 120 ms length
Step 6: FFT of correlation operation result
And (4) performing FFT operation on the correlation result after the operation in the step (5), and performing Q-point FFT operation (wherein Q is more than or equal to M) for P times N times in each capturing.
And 7: performing modulo operation on FFT result and outputting capture result
And performing modulo operation on the FFT result, comparing the maximum values of the P, N and Q FFT output results, and keeping the code phase value and the Doppler frequency value corresponding to the maximum values and the maximum values. And finally, comparing the maximum value with the threshold, if the maximum value is larger than the threshold, carrying out traction, and if the maximum value is smaller than the threshold, judging that the capture fails.
The algorithm is implemented on an FPGA, where M is 40, N is 20, T1 is 10, T0 is 0.25, and Q is 64. The phase difference between the input signal and the chip is set to be 1 clock cycle, and the frequency difference between the input signal and the local carrier wave is 2000 Hz. The final capture peak is 13894, and the corresponding 2-ary representation of the capture address is 11' b00001100000, where the lower 6 bits represent the doppler frequency corresponding to 2000Hz and the upper 5 bits correspond to a chip offset of 1, as can be obtained by the simulation of modsim10.1a. The simulation result is consistent with the input signal of the preset testbench.
Claims (10)
1. A high-sensitivity satellite navigation fine-capturing method is characterized by comprising the following steps: the method comprises the following steps:
step 1: generating a channel local code and setting a carrier frequency;
step 2: i, Q two-path mixing results are generated;
and step 3: I. performing multi-path short-time correlation operation on the Q two paths of signals and a local code;
and 4, step 4: storing the result of the multi-path correlation operation;
and 5: carrying out correlation operation on the short-time correlation result and the data jump coefficient;
step 6: performing FFT on the correlation operation result;
and 7: and performing modulus operation on the FFT result and outputting a capturing result.
2. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 1 comprises the following operations:
the code phase obtained by rough capture is placed into a tracking channel, the channel code phase is delayed by stopping a channel code generator (the long code is the code generated by a chip waiting for the time to be placed in a relevant chip), and the local code is adjusted to be advanced by the rough capture result by L chips;
and obtaining Doppler frequency f0 according to coarse capture, placing f0 in a tracking channel, adjusting the carrier frequency of the corresponding tracking channel to be f (initial frequency of a local carrier) + f0, and simultaneously generating I, Q two paths of orthogonal carrier signals of corresponding frequency.
3. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 2 comprises the following operations:
and performing correlation operation on the I, Q two paths of orthogonal carrier signals and the intermediate frequency signal to generate I, Q two paths of mixing signals.
4. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 3 comprises the following operations:
and carrying out N-path chip delay on the local code output by the tracking channel to generate N-path parallel code output, carrying out correlation operation on the N-path parallel code and the input I, Q two-path signals, respectively carrying out N-path short-time accumulation on N-path parallel correlation results, and finally delaying and outputting the N-path short-time accumulation results.
5. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 4 comprises the following operations:
outputting N groups of short-time correlation results to the RAM after each acc _ complete (the signal is a first short-time correlation completion mark) is high, completing the write operation after N clocks, and performing M write operations by capturing once, wherein the depth of the RAM is M x N.
6. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 5 comprises the following operations:
and correspondingly multiplying the short-time correlation result cached in the RAM by a data jump coefficient prestored in the ROM to generate a new short-time correlation result.
7. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 6 comprises the following operations:
and (5) performing FFT operation on the data subjected to correlation operation in the step (5), and performing Q-point FFT operation (wherein Q is more than or equal to M) for P times N times in each capturing.
8. A high-sensitivity satellite navigation fine-capturing method as claimed in claim 1, wherein: the step 7 comprises the following operations:
and performing modulus operation on the FFT result, comparing the maximum value, and keeping the capture code phase value and the Doppler frequency value corresponding to the maximum value.
9. The high-sensitivity fine satellite navigation capturing method according to claim 4, wherein: and 3, performing N-path chip delay on the local code output by the tracking channel in the step 3 to generate N-path parallel code output, performing correlation operation on the N-path parallel code and the input I, Q two-path signals, performing N-path short-time accumulation on N-path parallel correlation results respectively, and finally completing marking control on the delayed output of the N-path short-time accumulation results through N-path short-time correlation.
10. A high-sensitivity fine satellite navigation capturing method as claimed in claim 6, wherein: in the step 5, the short-time correlation result cached in the RAM is correspondingly multiplied by a data jump coefficient prestored in the ROM in advance to generate a new short-time correlation result.
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